1. Field of the Invention
The present invention relates to a ground fault detecting system for detecting a ground fault or an insulated state of an ungrounded power supply with respect to a grounded region (ground), and an electric vehicle incorporating such a ground fault detecting system.
2. Description of the Related Art
Generally, electric vehicles carry a power supply having a high voltage, which is of 200 [V] or higher, for example, insulated from the vehicle body as an ungrounded power supply.
There has been proposed a technology for detecting a ground fault (including a ground leakage or a lowered insulation resistance value due to a deteriorated insulation) of such a high-voltage ungrounded power supply (see, for example, Japanese Laid-Open Patent Publication No. 08-226950).
According to the technology disclosed in Japanese Laid-Open Patent Publication No. 08-226950, a storage battery as an ungrounded power supply is electrically connected to a propulsive motor via a circuit breaker, and a ground fault detector is connected parallel to the motor.
On the electric vehicle disclosed in Japanese Laid-Open Patent Publication No. 08-226950, electric power (counterelectromotive force) regenerated by the motor is supplied to charge the storage battery. Therefore, the counterelectromotive force generated by the motor is kept essentially as high as the voltage across the storage battery.
If the circuit breaker operates to disconnect the storage battery from the motor while the motor is operating in a regenerative mode, then a high regenerative voltage (counterelectromotive force) from the motor is applied to the ground fault detector, tending to break or damage circuit components of the ground fault detector.